The present invention relates to a shift lock system for an automatic transmission.
One conventional shift lock system is shown in FIGS. 16.about.21. This shift lock system is mounted on a motor vehicle equipped with an automatic transmission, and includes a shift lever 701 of the automatic transmission, a rotary bush 703 provided at the lower portion of the shift lever 701, and an electromagnetic actuator including a shift lock solenoid 705.
The rotary bush 703 is provided below a lock pin 707, and rotatable between a lock angular position and an unlock angular position. The rotary bush 703 has an unlock recess 703a, which allows the lock pin 707 of the shift lever 791 to move downward when the rotary bush 703 is in the unlock position.
The rotary bush 705 is connected with a solenoid rod 705a of the shift lock solenoid 705. The solenoid rod 705a is urged in a projecting direction by a spring 730 schematically shown in FIG. 21.
The shift lock solenoid 705 is electrically connected with a controlling means which includes a shift lock control unit 732 for energizing and deenergizing the shift lock solenoid 705 in accordance with signals sent from various switches and sensors 733 (serving as a sensing means). In this example, the shift solenoid 705 is off when a key switch (or ignition switch or vehicle main switch) is in an on position, and a brake pedal of the vehicle is not depressed. In this state, the spring 730 (serving as a resilient means) applies a spring force to the solenoid rod 730, thrusts the solenoid rod 730 outward, and by so doing holds the rotary bush 703 in the lock position as shown in FIG. 16. In this position, the unlock recess 703a of the rotary bush 703 is not located just below the lock pin 707, and the upper end of the rotary bush 703 makes it impossible to lower the lock pin 707. The driver cannot lower a compression rod 713 by pushing a release button 711 of the shift lever 701, and cannot shift the shift lever 701 from the parking position.
When the key switch is in the on position and the brake pedal is depressed, the shift solenoid 705 becomes on and rotates the rotary bush 703 to the unlock position by withdrawing the solenoid rod 705a, In the unlock position, the unlock recess 703a is aligned with the lock pin 707 and allows the downward movement of the lock pin 707. By this downward movement, the lock pin 707 is moved out of a groove formed in a position plate 709 and the shift lever 701 is allowed to move from the parking position.
When the shift lever 701 is away from the parking position, a detent switch is on, and accordingly, the shift lock solenoid 705 is off. Therefore, the spring 730 tries to return the rotary bush 703 to the lock position. However, a lock lever 715 is arranged to prevent the rotary bush 703 from returning to the lock position. As shown in FIG. 17, the lock lever 715 is loaded by a spring 717, and has a first arm 715a for abutting on a stopper 719 and a second arm for abutting on an abutment wall 703b of the rotary bush 703. When the shift lever 701 is in the parking position, the stopper 719 abuts on the first arm 715a, and holds the second arm 715b away from the abutment wall 703b of the rotary bush 703. When the shift lever 701 is moved from the P position toward the R (reverse) position as shown in FIG. 18, the lock lever 715 is moved away, and released, from the stopper 719. Therefore, the lock lever 715 is rotated by the force of the spring 717 and holds the rotary bush 703 in the unlock position to allow the shifting of the shift lever 701, by pushing the abutment wall 703b of the rotary bush 703 with the second arm 715b. When the shift lever 701 is returned to the parking position, the first arm 715a of the lock lever 715 comes in contact with the stopper 719 again, and accordingly, the rotary bush 703 rotates by the action of the spring 730 to the lock position.
This conventional shift lock system further includes a cancel arrangement for allowing the driver to unlock the shift lever 701 even if the shift lock solenoid 705 becomes unable to unlock the shift lever. As shown in FIGS. 19A.about.20B, this cancel arrangement includes a cancel lever 721 and a cancel knob 723. The cancel lever 721 has a pivoted portion 721a which is rotatably supported on the shift lever 701, and an arm having an end 721b confronting the abutment wall 703b of the rotary bush 703. A spring 725 normally holds the cancel lever 721 in the non-cancel position shown in FIGS. 19A and 19B. The cancel knob 723 extends along the shift lever 701, and has a lower end linked with the cancel lever 721 and an upper end which is exposed a little in front of the shift lever 701 in the passenger compartment.
If the shift lock solenoid 705 fails because of a trouble in the electrical circuit, then the rotary bush 703 is immovable in the lock position, and the shift lever 701 remains locked in the park position even if the key switch is on and the brake pedal is depressed. In this awkward situation, the driver is still able to unlock the shift lever 701 manually by pushing the cancel knob 723. When the cancel knob 723 is pushed down in the lock state shown in FIGS. 19A and 19B, the cancel lever 721 swings down against the force of the spring 725 as shown in FIG. 20A, and forcibly rotates the rotary bush 703 to the unlock position by pushing the abutment wall 703b with the arm end 721b. This cancel knob 123 can be readily operated by hand without any special tool.